Field of the Invention
The present invention relates to an image recording apparatus which generates a predetermined amount of line data in accordance with image information and which uses this line data to record an image on a recording medium, thereby recording the image.
A facsimile apparatus having thermal transfer printing means is one known type of such an image recording apparatus. This facsimile apparatus intermittently records whereby data for one line is recorded each time one line's worth of data has been generated from received information and transferred to a line recording head. Consequently, recording interval between recording one line and recording the next line will vary according to the quantity of coded line data. In fact, the recording interval frequently varies by three orders of magnitude, from as little as several milliseconds to as much as several seconds. Therefore, various measures are taken in regard to application of heat after the completion of one-line recording, such as post-heating, in order that all lines will be recorded under uniform and optimum rate of application of heat.
It is, however, not easy to optimize the rate at which recording heat energy is applied for each of line of recording regardless of the varying time intervals between successive recording lines. In addition, image quality tends to be degraded by such irregular operation, as when, for example, sticking occurs as a result of irregular operation of the recording paper feed motor, which irregular operation may be caused by the variations in the recording interval.
A recording method known as the "multi-print method", employs a type of ink sheet known as the "multi-print sheet" which is usable "n" times. For performing a continuous recording over a length L, the multi-print sheet is fed by a distance which is smaller than L either during or after image recording. The length of feed of the multi-print sheet is represented by L/n, n being greater than 1. In use, the ink layer on the ink sheet is subjected to "n" cycles of heating, so that a portion of the ink layer is melted in each heating cycle, and the melted portion of the ink sheet is transferred to the recording paper due to the shearing force between the melted portion of the ink and the portion of the ink which has not been melted. The discontinuous motor operation due to the above-mentioned variations in the recording intervals causes a change in the shearing force between the melted and solid portions of the ink, depending the quality of the recorded image due to, for instance, sticking.
When the time interval between the recording of one line and the recording of the next line is long, the ink temperature is lowered so that the shearing force needed to separate the melted portion of the ink from the solid portion is increased making it more difficult to separate the ink sheet from the recording paper.
A recording method also is known in which heat-sensitive recording paper is selectively heated by a thermal head which is energized in accordance with image signals, so that selected portions of the heat-sensitive recording paper change color, recording the information. Another known method is the "single print method" which employs an ink sheet composed of a base film and a layer of thermally fusible ink applied to the base film, the ink sheet being selectively heated by a thermal head so as to melt and transfer the ink to the recording paper. The problems just described in connection with the multi-printing method are also encountered with these recording methods, although they may be less not serious than in the case of multi-printing method. The above-mentioned problems caused by the variations in the recording time interval are also encountered in other types of recording systems such as, for example, ink jet printers in which information is recorded by a jet of ink droplets, the ink being driven by a change in the state of the ink which is caused by boiling the ink by the selective application of heat, since such intermittent recording requires intricate controls of heating and feed of the recording medium, again degrading the recorded image quality.